Problem with one zone

Hi,
I have a 12 zone system which works fine except for one zone. When this zone turns on, the pump switches on and off several time in quick succession, and then will run for about 10-15 seconds, and then go back to this rapid switching on and off, then back to running for 10-15 seconds again. Water is dribbling out of the sprinklers in this zone when this is happening.